Constant power regulator for hydraulic pumps

ABSTRACT

A variable displacement pump including pressure-compensated means for operating a pump-adjusting mechanism to vary the displacement of the pump and spring means yieldingly opposing the pressure-responsive means. A pressure is provided which is responsive to the effective position of the pump-adjusting mechanism and works in unison with the spring means.

United States Patent [72] Inventor Kurt R. Lonnemo [50] Field of Search 103/38, Troy, Mich. 38A, 161A, 162A, 120A, 120C, 12OPA; 230/20, [21] App]. No. 779,881 177, 138, 178; 92/131 [22] Filed Nov. 29,1968 [45] Patented Jan. 12, 1971 References Clted [73] Assignee Sperry Rand Corporation i UNITED STATES PATENTS y f- 2,283,321 5/1942 Doe et a] lO3/38iK g gzg Delaware 2,903,852 9/1959 Bottoms 103/162X Pnomy gr i Primary ExaminerRobert M. Walker [31] No. 16593/67 Attorney-Barnes, Kisselle, Raisch & Choate inc luding pressure-compensated means for operating -a pump-adjusting [54] CONSTANT POWER REGULATOR FOR mechanism to vary the displacement of the pump and spring HYDRAULIC PUMPS means yieldingly opposing the pressure-responsive means. A 24 Chums 4 Drawmg pressure is provided which is responsive to the effective posi- [52] U.S.CI. 92/l3.l tion of the pump-adjusting mechanism and works in unison [51 Int. Cl. F04b 49/00 with the spring means.

PATENTEDJAHIZIQ?! 3554.093

INVENTOR KURT R. LONNEMO ATTORNEY PATENIEUJAHIPIHYI 3554093 SHEETUUFLI INVENTOR KURT R. LONNEMG ATTORNEY CONSTANT POWER REGULATORFOR HYDRAULIC PUMPS Hydraulic pumps with continuously variable displacement are known in a number of different designs and are used principally to deliver pressure fluids to hydraulic power transmission units. Usually these pumps are of the axial or radial piston-type, and are fashioned to operate at high pressure, and

it is a common feature of all of them that the continuous variamechanism which is actuated by the action of the pump outlet pressure on'a movable contact surface and, in the opposite direction, by a spring unit, and which controls a selective pressure liquid supply to the actuating device in such a way that, when the pump outlet pressure rises above the value determined by the choice of spring unit, the device automatically actuates the adjusting mechanism in such a way that the displacement of the pump is diminished, and vice versa. This type of regulator is usually called a pressure-compensating device and also exists in certain variants, in which the valve mechanism is acted upon in the second direction, not only'by the spring unit, but also, either direc'tly'by the hydraulic pressure which operates the actuating device, or by a secondary piston which, in turn, is acted upon by the pressure of said device or by the pump outlet pressure;

It is also a known practice to equip hydraulic pumps, with a continuously variable displacement, with regulators which provide an, at least approximate, constancy of the pumpoutput by automatically adjusting the displacement of the pump and, with it, the efilux, in accordance with the variations occurring in the pump outlet pressure. When the outlet resistance for a pump, so equipped, is increased, the pump outlet pressure rises continuously, (with a corresponding decrease in efflux from the pump), up to a certain maximum determined by' a pressure-limiting device, at which the pump displacement drops to approximately zero. If, later, the pump outlet resistance again drops, so that it-can be overcome by a lower pump outlet pressure than the maximum, the regulator assures that the efflux from the pump is adjusted immediately thereafter, doing so in such a manner that the power delivered by the pump or, if this is desirable, the power delivered to the pump by the drive motor,'isalways constant.

However, practice has shown clearly that considerable difficulty is involved in realizing such a constant power regulator, satisfactory'from all points of view, because, even though very complicated constant power regulators of this kind have been developed, it has been found to be impossible, with the known devices, to attain an ideal pressure-flow characteristic,

without substantial deviations or disturbances within at least some parts of the range of regulation. These complicated regulator constructions also are very expensive and sensitive to operating disturbances of various kinds. To this must be added the fact that possible changes in the power level usually are very complicated. All of this has, to a great extent, contributed to markedly limit the use of power regulators, even though these would be highly desirable in many respects.

The purpose of the present invention is to create a constant power regulator, in which the aforesaid disadvantages are eliminated entirely and by means of which an adjustable pressure-flow characteristic, regular and undisturbed over the whole range of regulation, is obtainable while using very sim-' ple and inexpensive means. Thus, viewed technically, the invention can be considered to be a further development and amplification of the previously mentioned pressure compensating devices, inasmuch as it, similar to them, is based on both a hydraulically operated device for actuating the pump adjusting mechanism, and also a valve mechanism which, in one direction, is acted upon by the action of the pump outlet pressure on one of the movable contact surfaces and, in the opposite direction, by a spring unit, as well as a cooperating hydraulic pressure which acts on the other contact surface. In most cases the first contact surface is disposed on the valve mechanism itself while the second may also likewise be disposed, but generally, instead, is fashioned as a so-called return" piston, separate from the valve mechanism. but acting upon it.

The characterizing feature of the constant power regulator according to the invention is that the pressure which works in unison with the spring unit is regulated by a pressure-varying device, as a function of the position of the pump-adjusting mechanism. The pressure which works in unison with the spring unit is thus varied in such a way that it increases, or decreases, in proportion to the pump outlet pressure and in step" with it, and inversely proportional to the increase, or decrease, in the pump displacement.

The force of the spring unit acting on the valve mechanism, which (force) expediently can be adjusted, in a manner in itself know, by presetting, determines, in the regulator according to the invention, not only the lowest pressure on the discharge side of the pump, at which the regulator is to commence operating, but also the power of the pump to be held constant, which brings about a far-reaching simplification of the adjustment of the power level. Because of the continuous interaction, during operation of the regulator between the pump outlet pressure and the controlled-pressure which works in unison with the spring unit, maximum uniformity in the pressure-flow characteristic is thus obtained, independent of the set magnitude of the power, and the need for complicated spring and limiting devices in the regulator, disappears completely. I

The pressure-varying device incorporated in the constant power regulator according to the invention preferably comprises at least one variable constriction and has its simplest and most appropriate form when the variable constriction is fashioned as a leakage slit of variable length between a slide member and an interacting sleeve which are so disposed as to proportionately change their relative positions, when the pump-adjusting mechanism moves. The maximum length of the leakage slit (s) that is the maximum attainable choke effect can thus easily be adjusted in a very advantageous manner, to include the desired adjustment of the pressureflow characteristic, depending on for example pump leakage or other factors. Of course, the characteristic can also be changed by a suitable choice of the relative magnitude of the two contact surfaces, by means of which the valve mechanism is operated by the regulated pressure which works in unison with the spring unit and the pump outlet pressure, respectively.

It has been found to be particularly advantageous to design the slide element with one active part of limited length dimensions in the direction of motion of the slide member relative to the sleeve, said active part communicating on one side with the pump inlet and, on the other side, with the pump outlet, and to design the part of the sleeve which functions with the active part of the slide element with a discharge opening for the regulated pressure which operates in unison with the spring unit, past which discharge opening the active part of the slide element is arranged to move in such a manner that, at least in some operating positions, a two-sided leakage slot is obtained, with relation to the discharge opening. Thus, from the beginning, the entire length of the leakage slot may be available between the discharge opening and the discharge side of the pump, but when the active part of the slide element later is displaced, due to a change in position of the pump-adjusting mechanism, that is due to displacement of the pump, the length of the leakage slot and the associated choke effect are distributed on both sides of the discharge opening. This assures a relatively easily calculated relation between the regulated pressure which functions together with the spring unit and the displacement of the slide element, thus simplifying the fitting of the regulator to various pumps.

A construction of the regulator, very advantageous for most practical requirements, is made possible if the slide element is fashioned as a body which can move axially in a cylindrical bore in the sleeve, and if the regulator actuating device has the form of a piston, in which case the slide element is conveniently disposed coaxially with said piston and in such a way that. by means of mechanical contact, the former follows the movements of the latter. Consequently, the construction of the regulator can be made extremely compact and can easily be incorporated in the pump housing itself, either completely or in part.

For further clarification of the invention, some embodiments of a constant power regulator according to the invention will be described in the following, in the light of the attached drawings. In connection therewith, additional features and properties of the object of the invention will be brought out.

In the drawings:

FIG. 1 shows, partly schematically and in section, one embodiment of the constant power regulator according to the invention, in which the pressure-varying device comprises a rectilinearly movable slide element.

FIG. 2, likewise partly schematic and in section, shows a second embodiment of the constant power regulator, in which the pressure-varying device includes a rotary slide element.

FIG. 3 shows, in turn, partly schematic and in section, a variant of the constant power regulator according to FIG. 1, assembled with an axial piston pump of a well-known type, readily available on the open market.

FIG. 4, finally, shows, in the form of a curve diagram, a representative example of the pressure-flow characteristic of a constant power regulator according to the invention, with some different settings and modifications of details.

In FIG. 1, 1 indicates a hydraulic pump with continuously variable displacement, shown only schematically, inasmuch as it may be of a type known in itself. The pump 1 has a discharge line 2, an inlet line 3 and in addition is provided with an adjusting mechanism 4, which in the drawing is conceived to be vertically movable and which, in a manner in itself known, acts on the pump so that the displacement of the latter, and with it also the efflux, is decreased at a constant rotary speed, when the adjusting mechanism 4 is pushed downward, and vice versa. The regulator itself, which in general is designated by 5, is connected by a line 6 to the discharge side of the pump 1 and to the inlet side of the pump by means of a line 7. In actual practice the regulator and pump are often joined together in such a way that the lines 6 and 7 can be replaced by short channels.

The regulator itself comprises a housing or sleeve 8, in which is disposed a borehole 9, in which a slide 10, serving as a valve mechanism, is axially movable. The line 6 connects with the lower end of borehole 9, and from this emanates another channel 11, the purpose of which is to be described later. A little above its lower end, borehole 9 is crossed by another bore 12, which. via a channel [3, communicates with a third borehole 14 in the regulator housing and also via a branch line 13'. A bit farther up, borehole 9 communicates again, via channel 15, with borehole l4 and, in addition, with the discharge side of a pressure-limiting valve 16, incorporated in the regulator housing. In an upward direction, borehole 9 opens into a larger bore 17, the upper end of which is sealed by a threaded plug 18, which can be screwed in or out and thus serves as an adjusting device.

Approximately midway between its ends, the slide 10 is provided with an annular flange 10' which has an insignificantly larger axial thickness than borehole 12 and the upper end of the slide is, in addition, equipped with a cap 10" which is guided in the upper end section of borehole 9, without completely blocking it. The cap 10 makes contact in the larger bore 17 with a connecting piece 19 which is subject to the action of a spring 20, the upper end of which rests against the plug 18 and which tries to force the connecting piece 19, and with it also the slide 10, in a downward direction. Independent of spring 20, the connecting piece I9 is acted upon. at its upper end, by a secondary piston 21 which moves axially in a borehole 22 in the lower end of plug 18. The plug 18 has double, axially separated, seals 23 and 24, against the surrounding parts of the regulator housing 8. and the upper part of bore 22 communicates, via the interspace between these seals, and via a channel 25, both with the inlet side of the pressure-limiting valve 16 and with an annular recess 26 in bore 14.

In the borehole 14 is disposed a lengthy slide element, generally designated by 27. This slide element has the form of a relatively thin rod, the lower part of which forms a shaft 28, and the upper part of which is provided with three, axially separated, cylindrical enlargements 29, 30 and 31, respectively, of which the lowest 29 and the uppermost 31 have a suffciently large diameter to act as a seal, at least substantially, with the wall of borehole 14, as the slide element moves along axially, while the middle enlargement 30 expediently has asomewhat smaller diameter so that between the same and the wall of borehole 14 an annular leakage gap 32 is formed. The upper end of slide element 27 works in unison with a spring 33 which seeks, with a moderate force, to push the slide element downward in the HQ, and the shaft 28 of the slide element rest 5, with its lower end, against an adjusting piston 34, which can move axially in a cylindrical chamber 36, against the action of a more powerful spring 35, said chamber forming a widened axial extension of borehole 14, The piston 34, via shaft 34', communicates directly with the pump-adjusting mechanism 4, in such a manner that the adjusting piston completely controls the location of the adjusting mechanism.

The channels 11, 13 and 15, respectively, leading from the borehole 9, open in such a way into the borehole 14 that the channel 11, which also communicates openly with the discharge side of the pump, opens between the two upper enlargements 31 and 32 of the slide element, while channel 13 opens beneath the lower slide element enlargement 29 and consequently communicates openly, via borehole 14, with the cylindrical chamber 36 above the adjusting piston 34, while at the same time communicating, via branch 13', with the upper end of borehole 14, above the upper enlargement of the slide element 31. In turn, channel 15 opens into the borehole 14 at a level between the lowest and middle slide element enlargement 29 and 30, respectively, and this part of borehole 14 is also connected to the inlet side of the pump, via line 7. This means that the upper side of the slide element enlargement 30, which forms the leakage gap, communicates with the inlet side of the pump, while its lower side communicates with the inlet side of the pump (SIC). The slide element 27 is also, at least approximately, balanced from the hydraulic point of view.

The slide 10 in borehole 9 in itself acts as a contact surface for the pump outlet pressure, which seeks to push the slide upward against the action of spring 20, inasmuch as the upper part of bore 9, as well as the larger borehole l7, are subject to the low inlet pressure of the pump. The annular flange 10 on slide 10 here serves, in conjunction with the transverse bore 12, as a selective valve device, which, on increase of the pump outlet pressure in lines 2 and 6, beyond a certain value primarily determined by spring 20, brings in pressure fluid into channel 13 and at the same time produces a motion of the adjusting piston 34 in a downward direction. If, on the other hand, the pump outlet pressure drops below the value determined by the spring 20, the slide 10, instead, moves downward and pulls out pressure fluid from the channel 13, via channel 15 and line 7 to the pump inlet side, so that the adjusting piston, acted upon by spring 35, moves upward. This operation is in itself well known from so-called pressure-compensating devices. Since, however, the slide element 27 follows the motion of the adjusting piston 34, the middle enlargement 30 of the slide element moves relative to the annular recess 26 in bore 14, so that the entire length of the leakage gap 32 is distributed on both sides thereof, and thus the fluid pressure in channel 25 is caused to vary proportionally with the motion of the adjusting piston 34. The thus regulated pressure in channel 25 acts on the secondary piston 21 which then seeks, by way of connecting piece 19, to force the slide downward-against the action of the pump outlet pressure. It should be noted that the secondary piston 21 acts parallel with, and not via, the' spring 20.

In this way the various parts of the regulator come to work together to maintain a certain relation between the outlet pressure of the pump 1 and its displacement, namely in such a way as is best brought out in FIG. 4, in which P designates the pump outlet pressure and Q designates the pump efflux at constant pump rotary speed, while the line Qmzu efines the pump efflux at maximum displacement. The continuously drawn curves A, B and C show the relation between the pump outlet pressure and the pump efflux, at different power levels, as set by the regulator. These levels are determined by the tension in spring in the regulator and thus (at least within certain limits) can be chosen continuously be screwing the plug 18 into or out of the regulator housing 8. It should be noted that the maximum pressure for each power level is limited, which is accomplished by means of the fixed adjustment of the pressure-limiting valve 16, which provides a limitation of the pressure in the system, without loss of power, because it operates between the regulated pressure in channel 25 and the pump inlet side. Of course, the pressure-limiting valve 16 could be adjustable, and it might also be replaced by an ordinary overflow valve, situated in a suitable manner between the outlet and inlet sides of the pump.

As is made evident by the alternative curves B and B" respectively (broken line and dot-dash) it is possible, by making certain variations in the regulator, to adjust the pressureflow characteristic according to the pump leakage and other factors. Naturally, in such a case, these adjustments occur at all power levels, although these will not be shown, for the sake of clarity. Curve 8' can be obtained either by increasing the area of the secondary piston 21 in relation to the'contact area on slide 10, acted upon by the pump outlet pressure, and/or by shortening the length of the middle enlargement (which forms the leakage gap) on slide element 27, so that it becomes shorter than the stroke of adjusting piston 34. Correspondingly, Curve B" is obtained by decreasing the area of the secondary piston, in relation to the contact area on slide 10 and/or by making the enlargement'30 longer than the stroke of the adjusting piston.

The constant power regulator shown in FIG. 2 does not differ substantially, from a functional point of view, from the one shown in FIG. 1, but has partly assumed another structural design, due to the fact that the pump 1 is assumed to be of such a type that its adjusting mechanism 4 can expediently be fashioned as a rotary shaft which acts on the adjusting piston 34 of the regulator, via a rack 38 and pinion 37. Then the shaft 4' continues beyond the pinion 37 and is directly connected with a rotary slide 39 which operates in a separate sleeve 40, which (because of technical aspects of drawing) is shown apart from the actual regulator housing 8, although in actual practice it can certainly be incorporated therein. The details included in the regulator housing B can correspond in all respects to those shown in FIG. 1 on the right side of the regulator housing B and they are therefore given the same symbolic notation as before and need not again be described here. The channels l1, l5 and 25 lead to the sleeve 40 and they open into a cylindrical chamber 41, disposed therein, for the rotary slide 39. The rotary slide is provided with two axially extending recesses 42 and 43, respectively, between which is located a protrusion 44 which expediently may have a somewhat smaller radius than the remainder of the rotary slide, thus forming a leakage gap 45 between the recesses 42 and 43 and the outlet of channel 25. Otherwise, the rotary slide 39 satisfactorily seals against the sleeve 40, and is not substantially affected by any torque produced by the pressure exerted on the working chamber 41.

It should be clear, without further comment, that if the pressure on the outlet side of the pump rises sufficiently to actuate the adjusting piston 34 to move downward against the action of the spring 35, this is accompanied by a rotary motion of shaft 4, which serves as adjusting mechanism for the pump, in such a direction that the displacement of the pump, and with it the efflux, is reduced. However, at the same time the rotary slideturns in such a waythat the pressure channel 25, and therefore on the left side of secondary piston 21. increases and slide 10 is forced to the right, not only by spring 20 but also by piston 21, namely with such a force as is inversely proportional to the pump displacement. However, if the pump outlet pressure drops, the pressure on the secondary piston comes down again and the overall effect is that the desired pressureflow characteristic obtained is in accordance with the curves shown in FIG. 4. In this case also, the pretension on spring 20 is the factor which determines the power level and the lowest pressure at which the regulating function begins. The pressure-limiting valve 16 limits the maximum pressure in the same manner as before.

In the regulator of FIG. 2 the length of the leakage gap is of course determined by the peripheral width of the protrusion 44, between recesses 42 and 43, that is by the angle a and this is therefore what is changed, when required, to adjust the characteristic of the regulator in relation to the leakage of a given pump and other factors affecting power. As before, however, this adjustment can also be made alternatively by changing the area of the secondary piston 21 in relation to the slide 10, which may be more convenient, inasmuch as the plug 18 and the corresponding piston are easily interchangeable.

Instead of having the rectilinearly movable adjusting piston 34 in FIG. 2 act on the rotary adjusting mechanism 4 by way of the rack 38 and pinion 37, it is of course possible to join channel 13 to a rotary motor which acts directly on the adjusting shaft 4'. In that event this motor can be designed directly so as to function as the above-described rotary slide 39. Such a possibility is indicated, but not worked out, in FIG. 2 and would be realized if channel'13 were connected to inletchannel 46 in sleeve 40. The adjusting piston spring 35 would in this case be replaced by any suitable spring (not shown) which would act on the rotary slide in a clockwise direction.

In the example according to FIG. 3 a variant of a constant power regulator is shown, which is particularly suitable for use with, and assembled as a unit with, an axial piston pump with continuously variable displacement, of the usual type available on the market. Inasmuch as a certain knowledge of the construction of the pump will facilitate understanding of its operation, the pump itself is shown in detail, in schematized form. The principal components thereof comprise a pump housing 50 with a pump housing cover 51. A drive shaft 52 is mounted in the pump housing and cover and supports a rotor 53 which houses an annular series of pump cylinders 54 each of which incorporates an axially movable pump piston 55. Each pump cylinder 54 has an opening 56 at its upper end and these openings, as the rotor turns, function, in a manner like that of a slide valve, with the pump housing cover 51, in which are disposed curved bends with inlet and outlet channels, not shown in the drawing. The pistons 55 in the different cylinders 54 work in unison with an obliquely set yoke 57 in such a manner that, as the rotor revolves, they produce an axial backand-forth motion. The yoke 57 is pivoted in the pump housing 50 around pins represented by center 58 and is actuated on one side by a powerful spring 59 so as to assume the oblique position shown, when under no pressure. However, the yoke 57 can swing clockwise against the action of spring 59, around its supporting pins at 58, so that the upper side of the yoke lies in a plane perpendicular to the drive shaft and the rotor 53. With such a position of the yoke, the axial motion of pistons 55, and thus the pump displacement, is reduced to zero. Thus. the pump displacement is continuously variable, and the yoke 57 represents, in fact, the pump-adjusting mechanism. It should further be stated that the entire pump housing 50 is filled with the oil which is to be pumped, and thus the pressure on this oil can represent the pump inlet pressure. Although this is not immediately evident, this pressure also prevails in the channel 60 shown in cover 51, while channel 61 in the cover is connected, in a mariner not shown, with the outlet side of the pump, and thus the pump outlet pressure prevails in it.

Incorporated in the pump housing cover 51 there is a conconceivable, without departing from the basic idea of the invention. Therefore, the invention should not be considered to be limited to the embodiments shown and described. the only purpose of which is to illustrate and facilitate an understandstant power regulator, the housing of which, for the sake of ing ofthe inventive concept.

convenience, consists of three parts, namely an outer part 62, a central block 63 and a tubular sleeve 64 for the slide element. To facilitate an understanding of the regulator, the parts and channels have been given the same designations as in FIG. 1, but followed by an a Thus, the channel 61 in the pump housing cover 51 is connected to a channel 6a, the upper end of which opens into a borehole 9a, enclosing a slide 10a, of the same type as in FIG. 1 and FIG. 2. The top of slide 10a makes contact, inside a larger bore 17a, with a connecting piece 19a, which is acted upon by a spring 20a, which, in turn, bears against a plug 18a, adjustable by screwing in or out. Centrally in the plug is disposed a return piston 21a, in a borehole 22a. The first-mentioned bore 9a communicates via a channel 150 with channel 60 in the pump housing cover 51, where, as was previously stated, a pressure comparable with the pump inlet pressure prevails. The annular recess 12a which works in conjunction with the annular flange l0'a on slide 100, communicates with a channel 13a, which may be said to be extension of borehole 14a in the tubular sleeve 64 of the slide element. In the latter sleeve there is also disposed a transverse hole 7a which puts the borehole 14a into open communication with the interior of the pump housing and thus guarantees the pump inlet pressure in part of the bore.

The slide element itself 27a in this case has the form of a tube, the interior of which forms a prolongation of channel 13a and allows pressure oil from the annular recess 12a to penetrate down to the lower end of the slide clement 27a and thus not only to balance the slide element but also to act on the adjusting piston 34, which in this case encloses the lower part of the sleeve 64 like a shell and is guided by it, exerting its action directly on the yoke 57. The tubular slide element 27a is fashioned with three axially separated enlargements, namely a lower enlargement 29a, which provides a sliding seal in borehole 14a, a centrally located enlargement 30a and an upper enlargement 31a, which likewise forms a sliding seal in borehole 140. As in FIG. 1, an annular leakage gap 32 is disposed around the middle enlargement 30a, which expediently can have a somewhat smaller diameter than the other two, and enlargement 30a is here also designed so that, as the slide element moves vertically, it works in unison with an annular recess 26a in borehole 14a. This annular recess 26a communicates, via a line 25a (indicated in broken lines) with the return piston 21a, on its left side. The slide element 27a is acted upon by a spring 33a, downward as shown in the drawmg.

As must already have been made evident by the symbolic notation used, the constant power regulator shown in FIG. 3 is, in principle, constructed in the same way as the regulator according to FIG. I, and in operation is also equivalent. The adjusting piston spring 35, shown in FIG. 1, is represented in FIG. 3 by the spring 59. An increased outlet pressure in the pump seeks to push the slide 10a to the left, so that pressure fluid is fed to the adjusting piston 34a, whereon it seeks to decrease the slope of yoke 57 and, with it, the displacement of the pump. However, the slide element 27a accompanies the movement of the adjusting piston and, due to the decreased length of the leakage gap about the annular recess 26a, lowers the pressure on secondary piston 210, so that a new equilibrium position is reached immediately, corresponding to the increased pressure. A corresponding turn of the yoke 57 leads to decrease in the pump displacement and, with it, the efflux, so that the power input or output of the pump remains constant, according to the detailed dimensioning of the regulator, as was previously described. A decrease in the pump outlet pressure involves an inverse operation, so that the pump efflux again increases.

It should be clearly evident from the examples described that a large number of modifications and changes in detail are Iclaim:

1. The combination comprising:

a variable displacement pump;

pressure compensated means for varying the displacement of the pump including a pump-adjusting mechanism; means responsive to the outlet pressure of the pump for moving said pump-adjusting mechanism;

spring means yieldingly opposing said last-mentioned pressure-responsive means; and

secondary means responsive to the effective position of said pump-adjusting mechanism operable to apply hydraulic pressure and function in conjunction with said spring means to yieldingly oppose said pressure-responsive means.

2. The combination set forth in claim 1 wherein said secondary means comprises at least one variable constriction.

3. For use with a variable displacement pump including:

a pump-adjusting mechanism;

pressure compensated means for varying the displacement ofthe pump including a pump-adjusting mechanism; means responsive to the outlet pressure of the pump for moving said pump-adjusting mechanism;

spring means yieldingly opposing said last-mentioned pressure-responsive means; and

secondary means responsive to the efi'ective position of said pump-adjusting mechanism operable to apply hydraulic pressure and function in conjunction with said spring means to yieldingly oppose said pressure-responsive means.

4. The combination set forth in claim 3 wherein said secondary means comprises at least one variable constriction.

5. The combination comprising:

a variable displacement pump;

pressure compensated means for varying the displacement of the pump including a pump-adjusting mechanism; means responsive to the outlet pressure of the pump for moving said pump-adjusting mechanism;

spring means yieldingly opposing said last-mentioned pressure-responsive means;

secondary means responsive to the effective position of said pump-adjusting mechanism operable in conjunction with said spring means to yieldingly oppose said pressure responsive means;

wherein said secondary means comprises at least one variable constriction;

wherein said variable constriction comprises:

a body; a slide element;

said variable constriction comprising at least one leakage gap between said body and said slide element; and

said slide element being movable in response to movement of said pump-adjusting mechanism.

6. The combination set forth in claim 5 wherein said slide element has an active portion communicating on one side of the pump inlet and on the other side with the pump outlet, that portion of the body which operates in unison with the active portion of the slide element being provided with a discharge opening extending to said secondary means.

7. The combination set forth in claim 6 wherein the active portion of said slide element is disposed to move in a manner such that in at least certain operating positions a double leakage path is obtained with reference to the discharge opening.

8. The combination set forth in claim 5 wherein said body has a cylindrical bore, said slide element having a shape corresponding to said cylindrical bore.

9. The combination set forth in claim 5 wherein said pumpadjusting mechanism comprises a piston, said slide element being disposed coaxially with said piston and engaging said piston so that itmoves in conjunction with said piston.

10. The combination comprising: i

a variable displacement pump;

pressure-compensated means for varying the displacement of the pump including a pump-adjusting mechanism;

means responsive to the outlet pressure of the pump for moving said pump-adjusting mechanism;

spring means yieldingly opposing said last-mentioned pressure-responsive means;

secondary means responsive to the effective position of said pump-adjusting mechanism operable in conjunction with said spring means to yieldingly oppose said pressureresponsive means; v

wherein said pressure responsive means comprises a spool;

' a body having a bore within which said spool is reciprocated;

a passageway extending from the pump outlet to one end of said spool; 1

said spring means acting on the other end of said spool;

wherein said secondary means comprises a second spool associated with said first-mentioned spool;

a third spool; and

a passageway controlled by said third spool and extending to the end of said second piston opposite said first-mentioned spool.

11. For use with a variable displacement pump including:

a pump-adjusting mechanism;

pressure-compensated means for varying the displacement (of the pump including a pumpadjusting mechanism;

means responsive to the outlet pressure of the pump for moving said pump-adjusting mechanism;

secondary means responsive to the effective position of said pumpadj'usting mechanism operable in conjunction with said spring means to yieldingly oppose said pressureresponsive means; Y I

wherein said secondary means comprises at least one variable constriction;

wherein said variable constriction comprises:

a body; a slide element;

said variable constriction comprising at least one leakage gap between said body andsaid slide element; and

said slide elementbeing movable in response to movement of said pump-adjusting mechanism. i

12. The combination set forth in claim ll'wherein said slide element has an active portion communicating on one side of the pump inlet and on the other side with the pump outlet, that portion of the body which operates in unison with the active portion of the slide element being provided with a discharge opening extending to said secondary means.

13. The combination set forth inclaim 12 wherein the active portion of said slide element is disposed to move in a manner such that in at least certain operating positions a double leakage path is obtained with reference to the discharge opening.

14. The combination set forth in claim 11 wherein said body has a cylindrical bore, said slide element having a shape corresponding to said cylindrical bore.

15. For use with a variable displacement pump including:

a pump-adjusting mechanism;

pressure-compensatedmeans for varying the displacement of the pump including a pump-adjusting mechanism; means responsive to the outlet pressure of the pump for moving said pump-adjusting mechanism;

spring means yieldingly opposing said last-mentioned pressure-responsive means;

secondary means responsive to the effective position of said pump-adjusting mechanism operable in conjunction with said spring means to yieldingly oppose said pressureresponsive means;

wherein said pressure responsive means comprises a spool;

a body having a bore within which said spool is reciprocated; H

a passageway extending from the pump outlet to one end of said spool; spring means acting on the other end of said spool; wherein said secondary means comprises a second spool us- 5 sociated with said first-mentioned spool;

a third spool; and a passageway controlled by said third spool and extending to the end of said second piston opposite said first-mentioned spool. 16. The combination comprising: a variable displacement pump; a pump-adjusting mechanism for varying the displacement of the pump; pressure-responsive means responsive to the outlet pressure of the pump for moving said pump-adjusting mechanism; spring means yieldingly opposing said pressure-responsive means; and secondary means responsive to theoutlet flow rate of the pump for applying a hydraulic pressure to said pressureresponsive means in conjunction with said spring means to modulate the pump-adjusting mechanism.

17. The combination set forth in claim 16 wherein said secondary means comprises:

a valve member having a first contact surface and a second contact surface;

said first contact surface being hydraulically connected to the pump outlet pressure;

said spring means acting on said second contact surface;

and

said valve member having hydraulic pressure applied thereto. I

18. Constant power regulator for those hydraulic pumps, the displacement of which is continuously variable by action of a movable adjusting mechanism, said regulator comprising both a hydraulically operated actuating device which acts on said adjusting mechanism, and also a valve mechanism which is actuated in one direction by the action of the pump outlet pressure on one movable contact surface, and in the opposite 40 direction by a spring unit, as well as by a hydraulic pressure which works in conjunction therewith and acts on the other contact surface, and which provides for such a selective feed of pressure fluid to the actuating device that, when the pump outlet pressure rises above a value determined by the choice of spring unit, it acts on the adjusting mechanism automatically in such a way that the displacement of the pump is decreased, and vice versa, characterized in that the pressure which works jointly with the spring unit is regulated by a pressure-varying device, depending on the position of the pumpadjusting mechanism, said pressure varying device comprising at least two variable constrictions to a discharge opening which communicates with the spring unit, one of said constrictions communicating with said pump inlet and the other of said constrictions communicating with said pump outlet, such that as the displacement of the pump-adjusting mechanism increases, the affect of the leakage gap on the inlet side of the pump is decreased and the effect of the leakage gap on the outlet side of the pump is increased.

19. Constant power regulator according to claim 18, 60 characterized in that the variable constrictions comprises at least two leakage gaps of variable length between a slide element and sleeve which works in unison with it, these being so disposed as to change their relative positions proportionally when the pump-adjusting mechanism is moved.

20. Constant power regulator according to claim 19, characterized in that the slide element has an active part of limited extent in the direction of motion of the slide element relative to the sleeve, said active part communicating on one side with the pump inlet and on the other side with the pump outlet, and that the part of the sleeve which works in unison with the active part of the slide element being provided with said discharge opening for the regulated pressure which works in conjunction with the spring unit,- past which discharge opening the active part of the slide element is disposed to 75 move, so that in at least certain operating positions a twopiston and so as to follow its inovements, due to mechanical contact.

23. The combination set forth in claim 20 wherein said slide element is axially movable.

24. The combination set forth in claim 20 wherein said slide element is rotatable. 

1. The combination comprising: a variable displacement pump; pressure compensated means for varying the displacement of the pump including a pump-adjusting mechanism; means responsive to the outlet pressure of the pump for moving said pump-adjusting mechanism; spring means yieldingly opposing said last-mentioned pressureresponsive means; and secondary means responsive to the effective position of said pump-adjusting mechanism opErable to apply hydraulic pressure and function in conjunction with said spring means to yieldingly oppose said pressure-responsive means.
 2. The combination set forth in claim 1 wherein said secondary means comprises at least one variable constriction.
 3. For use with a variable displacement pump including: a pump-adjusting mechanism; pressure compensated means for varying the displacement of the pump including a pump-adjusting mechanism; means responsive to the outlet pressure of the pump for moving said pump-adjusting mechanism; spring means yieldingly opposing said last-mentioned pressure-responsive means; and secondary means responsive to the effective position of said pump-adjusting mechanism operable to apply hydraulic pressure and function in conjunction with said spring means to yieldingly oppose said pressure-responsive means.
 4. The combination set forth in claim 3 wherein said secondary means comprises at least one variable constriction.
 5. The combination comprising: a variable displacement pump; pressure compensated means for varying the displacement of the pump including a pump-adjusting mechanism; means responsive to the outlet pressure of the pump for moving said pump-adjusting mechanism; spring means yieldingly opposing said last-mentioned pressure-responsive means; secondary means responsive to the effective position of said pump-adjusting mechanism operable in conjunction with said spring means to yieldingly oppose said pressure responsive means; wherein said secondary means comprises at least one variable constriction; wherein said variable constriction comprises: a body; a slide element; said variable constriction comprising at least one leakage gap between said body and said slide element; and said slide element being movable in response to movement of said pump-adjusting mechanism.
 6. The combination set forth in claim 5 wherein said slide element has an active portion communicating on one side of the pump inlet and on the other side with the pump outlet, that portion of the body which operates in unison with the active portion of the slide element being provided with a discharge opening extending to said secondary means.
 7. The combination set forth in claim 6 wherein the active portion of said slide element is disposed to move in a manner such that in at least certain operating positions a double leakage path is obtained with reference to the discharge opening.
 8. The combination set forth in claim 5 wherein said body has a cylindrical bore, said slide element having a shape corresponding to said cylindrical bore.
 9. The combination set forth in claim 5 wherein said pump-adjusting mechanism comprises a piston, said slide element being disposed coaxially with said piston and engaging said piston so that it moves in conjunction with said piston.
 10. The combination comprising: a variable displacement pump; pressure-compensated means for varying the displacement of the pump including a pump-adjusting mechanism; means responsive to the outlet pressure of the pump for moving said pump-adjusting mechanism; spring means yieldingly opposing said last-mentioned pressure-responsive means; secondary means responsive to the effective position of said pump-adjusting mechanism operable in conjunction with said spring means to yieldingly oppose said pressure-responsive means; wherein said pressure responsive means comprises a spool; a body having a bore within which said spool is reciprocated; a passageway extending from the pump outlet to one end of said spool; said spring means acting on the other end of said spool; wherein said secondary means comprises a second spool associated with said first-mentioned spool; a third spool; and a passageway controlled by said third spool and extending to the end of said second piston opposite said first-mentioned spool.
 11. For use with a variable dispLacement pump including: a pump-adjusting mechanism; pressure-compensated means for varying the displacement of the pump including a pump-adjusting mechanism; means responsive to the outlet pressure of the pump for moving said pump-adjusting mechanism; secondary means responsive to the effective position of said pump-adjusting mechanism operable in conjunction with said spring means to yieldingly oppose said pressure-responsive means; wherein said secondary means comprises at least one variable constriction; wherein said variable constriction comprises: a body; a slide element; said variable constriction comprising at least one leakage gap between said body and said slide element; and said slide element being movable in response to movement of said pump-adjusting mechanism.
 12. The combination set forth in claim 11 wherein said slide element has an active portion communicating on one side of the pump inlet and on the other side with the pump outlet, that portion of the body which operates in unison with the active portion of the slide element being provided with a discharge opening extending to said secondary means.
 13. The combination set forth in claim 12 wherein the active portion of said slide element is disposed to move in a manner such that in at least certain operating positions a double leakage path is obtained with reference to the discharge opening.
 14. The combination set forth in claim 11 wherein said body has a cylindrical bore, said slide element having a shape corresponding to said cylindrical bore.
 15. For use with a variable displacement pump including: a pump-adjusting mechanism; pressure-compensated means for varying the displacement of the pump including a pump-adjusting mechanism; means responsive to the outlet pressure of the pump for moving said pump-adjusting mechanism; spring means yieldingly opposing said last-mentioned pressure-responsive means; secondary means responsive to the effective position of said pump-adjusting mechanism operable in conjunction with said spring means to yieldingly oppose said pressure-responsive means; wherein said pressure responsive means comprises a spool; a body having a bore within which said spool is reciprocated; a passageway extending from the pump outlet to one end of said spool; spring means acting on the other end of said spool; wherein said secondary means comprises a second spool associated with said first-mentioned spool; a third spool; and a passageway controlled by said third spool and extending to the end of said second piston opposite said first-mentioned spool.
 16. The combination comprising: a variable displacement pump; a pump-adjusting mechanism for varying the displacement of the pump; pressure-responsive means responsive to the outlet pressure of the pump for moving said pump-adjusting mechanism; spring means yieldingly opposing said pressure-responsive means; and secondary means responsive to the outlet flow rate of the pump for applying a hydraulic pressure to said pressure-responsive means in conjunction with said spring means to modulate the pump-adjusting mechanism.
 17. The combination set forth in claim 16 wherein said secondary means comprises: a valve member having a first contact surface and a second contact surface; said first contact surface being hydraulically connected to the pump outlet pressure; said spring means acting on said second contact surface; and said valve member having hydraulic pressure applied thereto.
 18. Constant power regulator for those hydraulic pumps, the displacement of which is continuously variable by action of a movable adjusting mechanism, said regulator comprising both a hydraulically operated actuating device which acts on said adjusting mechanism, and also a valve mechanism which is actuated in one direction by the action of the pump outlet pressure on one movable contact surface, and In the opposite direction by a spring unit, as well as by a hydraulic pressure which works in conjunction therewith and acts on the other contact surface, and which provides for such a selective feed of pressure fluid to the actuating device that, when the pump outlet pressure rises above a value determined by the choice of spring unit, it acts on the adjusting mechanism automatically in such a way that the displacement of the pump is decreased, and vice versa, characterized in that the pressure which works jointly with the spring unit is regulated by a pressure-varying device, depending on the position of the pump-adjusting mechanism, said pressure varying device comprising at least two variable constrictions to a discharge opening which communicates with the spring unit, one of said constrictions communicating with said pump inlet and the other of said constrictions communicating with said pump outlet, such that as the displacement of the pump-adjusting mechanism increases, the affect of the leakage gap on the inlet side of the pump is decreased and the effect of the leakage gap on the outlet side of the pump is increased.
 19. Constant power regulator according to claim 18, characterized in that the variable constrictions comprises at least two leakage gaps of variable length between a slide element and sleeve which works in unison with it, these being so disposed as to change their relative positions proportionally when the pump-adjusting mechanism is moved.
 20. Constant power regulator according to claim 19, characterized in that the slide element has an active part of limited extent in the direction of motion of the slide element relative to the sleeve, said active part communicating on one side with the pump inlet and on the other side with the pump outlet, and that the part of the sleeve which works in unison with the active part of the slide element being provided with said discharge opening for the regulated pressure which works in conjunction with the spring unit, past which discharge opening the active part of the slide element is disposed to move, so that in at least certain operating positions a two-sided leakage gap, with reference to the discharge opening, is obtained.
 21. Constant power regulator according to claim 20, characterized in that the slide element has the shape of a body which can move axially in a cylindrical bore in the sleeve.
 22. Constant power regulator according to claim 21, in which the adjusting device has the form of a piston, characterized in that the slide element is disposed coaxially with said piston and so as to follow its movements, due to mechanical contact.
 23. The combination set forth in claim 20 wherein said slide element is axially movable.
 24. The combination set forth in claim 20 wherein said slide element is rotatable. 